Mention in project description that XO is an ESLint wrapper

[darkred]

With this PR I change the description in readme.md(1st phrase) and in package.json, from:
JavaScript/TypeScript linter with great defaults to:
JavaScript/TypeScript linter (ESLint wrapper) with great defaults
in order to better clarify/stand out that xo uses ESLint underneath, an already very popular and widely used JavaScript linter,
and that it's not a linter itself, like JSLint, JSHint, ESLint, etc,
something that might discourage a new user from trying it, if he sees it for the first time, and has never heard of it.

Currently, searching in GitHub and npmjs,
the description, as it is, and the tags used in npmjs,
might all give the wrong impression that it's the opposite:

screenshots:

GitHub search

npmjs dropdown

npmjs search

 
Thank you

[sindresorhus]

Good point 👍

[darkred]

Thank you for the merge and your great work!